This invention relates, in general, to semiconductor packages, including, but not limited to, a flip chip package for semiconductor die.
Flip chip packaging has been used in the past to provide many advantages over wire bonding. Flip chip mounting involves directly mounting a semiconductor die having conductive bumps onto a rigid substrate carrier having conductive pads that mate with the conductive bumps. This is in contrast to wire bonding, where the chip is bonded to a rigid substrate and wires are bonded to conductive pads on the chip. Flip chip provides for shorter interconnection lengths which results in lower inductance. Flip chip also provides for elimination of wire bond which results in elimination of wire bonding steps. A smaller package footprint is also obtained with a flip chip package. Further, a lower profile chip mounting results because wire loops are eliminated.
One problem with flip chip packaging is that it is subject to mechanical strain at the point where the bumps and the rigid substrate are in contact due to the differential thermal expansion between the chip and the rigid substrate. One solution to this problem is to mount the chip onto a flexible membrane. The flexible membrane approach allows the chip to remain reliable during differential thermal expansion, however, the flexible membrane is not suitable for chips that need to dissipate a lot of heat. Chips that need to dissipate a substantial amount of heat (1 Watt) need to be attached to a heat sink, a thermally conductive layer. The flexible membrane does not have this characteristic, and thus does not act as a heatsink. Thus, a new packaging approach is needed which is suitable for chips that need to dissipate heat.